The present invention relates primarily to an apparatus for coupling a driven prime mover to a drawn load, and more particularly, to a coupling apparatus having a resilient coupling component to attenuate the transmitted noise, shock and vibration that is normally conducted into the towing vehicle, and whose hitch is detachably removable.
The purpose of a hitch is to connect a towed load, such as a trailer or implement to a tow vehicle. The most common type of hitch in use today is the drawbar type of hitch.
There are at least five major load classifications, where a Class I rating can tow up to a 2,000 pound load; a Class II rating, up to a 3,500 pound load; and a Class III hitch is rated to haul up to a 5,000 pound load and is used to haul loads, such a car, boat, camper, or the like. For heavier loads, such as with a heavier boat or camper, a Class IV hitch, whose rating is up to a 7,500 pound load, would be required; a Class V hitch having a 10,000 pound rating.
Other than the tow vehicle and the trailer load, the other critical element is the hitch. Trailer hitches are rated according to the capacity of the load weight and tongue weight, where the load weight is referenced in terms of Gross Trailer Weight (GTW) and the tongue weight is the downward force exerted on the hitch ball. The tongue weight is usually calculated as being 10 to 15 percent of the maximum rated GTW. The tongue is usually formed from the V-shaped frame-rails that merge at the front of the trailer. The coupler of the trailer is what accepts the hitch ball.
At the trailer""s end of the hitch, there is just one variable to consider and that is the size of the ballxe2x80x94at the tow vehicle""s end of the hitch, there are several variables that are necessary to consider.
First, it is important that the hitch coupler ball on the trailer be matched to the proper size coupler ball; otherwise the latching mechanism may fail to retain the hitch on the ball. A safety chain can be used to keep the trailer connected in the event the hitch separates.
There are three common sizes of hitch coupler balls for passenger type vehicles; they are: 1xe2x85x9e-inch for use with towed weight loads of less that 2,000 of towed weight, a 2-inch coupler ball is used for towed weights up to 3,500 pounds and 2{fraction (5/16)}-inch coupler ball can be used with loads up to 10,000 pounds.
Regarding the tow vehicle side of the connection, there are also several items to consider. Today""s modern cars have bumpers that are not suitable for use as an attachment point for a hitch. The vast majority of hitches are mounted to the car chassis undercarriage or frame.
The most common hitch is the drawbar type, which bolts to the undercarriage of the tow vehicle and provides a receiver pocket into which a steel drawbar for the hitch is secured. This type of mounting arrangement is advantageous because the drawbar and hitch coupler ball can be easily removed when not in use.
A drawbar is a bar that joins a vehicle to a drawn vehicle or implement. The drawbar can also be enhanced beyond being just a straight piece of steel. A straight drawbar is subject to several disadvantages, the main one being the transmission of noise and rattles into the tow vehicle.
The following prior art discloses the various aspects in the design and use of the elastomerically coupled drawbar.
U.S. Pat. No. 2,011,817, granted Aug. 20, 1935, to H. S. Littlefield, discloses a flexible coupling, for use primarily in coupling trailers to automobiles and/or trucks, but also to having various other types of farm equipment coupled to tractors, mine cars coupled to locomotives, etc.
U.S. Pat. No. 2,136,440, granted Nov. 15, 1938, to G. H. Hufferd, discloses a trailer hitch having a resilient bushing seated therein. The bushing has a hole therethrough in communication with the open ends of the housing.
U.S. Pat. No. 3,961,813 granted Jun. 8, 1976, to O. L. Thomas, discloses a trailer hitch for coupling a draft vehicle to a drawn vehicle wherein the eye portion of the hitch includes a molded insert of flexible material having an axial bore extending therethrough adapted to receive the pintle portion of the hitch in coupling relation. The flexible insert completely surrounds the pintle and thus maintains the pintle in spaced relation from the eye for yieldingly restraining relative radial movement between the pintle and the eye during all phases of operation, including flexing in the vertical plane when the trailer is negotiating inclined ramps or the like.
U.S. Pat. No. 4,131,296, granted Dec. 26, 1978, to D. S. Strader, discloses a trailer hitch comprising a draw tongue adapted to extend from a trailer, a handle mounted for pivotal movement above the draw tongue, and a cable attached at one end to the handle and extending downwardly through the draw tongue to a hitch coupler which is carried for bodily movement upwardly and downwardly as a function of pivotal motion of the handle. A drawbar adapted to be attached to a towing vehicle is slotted to receive the hitch coupler and recessed to capture the coupler as pivotal movement of the handle moves the latter upwardly. A resilient bushing of elastomeric material is captured in compression between the drawbar and the draw tongue resiliently to permit relative movement in all planes and to damp road shock therebetween.
Presently, the above prior art teaches of a hollow resilient bushing made of an elastomeric material, mounted in a vertical direction, about a stud member. The resulting attenuation of noise and vibration that is conducted though the elastomeric member is proportional to the wall thickness of the elastomer cylinder, where the transmitted forces are attenuated only by the compressive forces acting outwardly in a radial direction from the inner surface of the resilient bushing.
What is needed is a means of incorporating a shock absorbing material into the drawbar, to provide a better ride quality to the passengers of the tow vehicle.
It is therefore an object of the present invention to provide for a drawbar to couple a driven prime mover to a drawn load, the drawbar having a longitudinally mounted elastomeric member communicating with an inner and outer housing, where the elastomeric member is resistant to any resultant shear forces.
It is another object of the present invention to provide for a drawbar to couple a driven prime mover to a drawn load, that reduces the shock, noise, bounce and vibration that are typically related when towing.
It is still another object of the present invention to provide for a drawbar to couple a driven prime mover to a drawn load, that reduces the amount of wear due to shock, noise, bounce and vibration that are typically related when towing.
It is still yet another object of the present invention to provide for a drawbar to couple a driven prime mover to a drawn load, that utilizes a resilient linear damping element to dynamically isolate the load disturbances from the driven vehicle.
It is a still another object of the present invention to provide for a drawbar to couple a driven prime mover to a drawn load, that uses a elastomerically cushioned hinge pin to further reduce the shock, noise, bounce and vibration that are typically related when towing.
It is a final object of the present invention to provide for a clamp to take up any play between the prime mover receiver tube and the drawbar tube. This clamping serves to direct all of the shock, noise, bounce and vibration that are typically related when towing through the elastomeric elements.
These as well as other objects and advantages of the present invention will be better understood and appreciated upon reading the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings.
The present invention is comprised of a square outer tube made of a low carbon steel that has the mechanical strength to withstand the hoop stress and additional forces occurring in all directions placed upon it principally by the elastomeric elements and the tow vehicle""s hitch receiver. The low carbon steel square outer tube is sized to fit over the industry standard receiver tube and to accept the hitch pin through the cross hole.
A square inner tube, also made of a low carbon steel, has an outboard end extension that is sufficient in length in relation to the outer tube to facilitate a weld attachment of various rise and/or drop tongues for balls, pintle adapter plates, and other connections commonly seen in the industry. Its inboard end extends beyond the surrounding elastomer element and also possesses a through slot. This slot is coincident with but larger than the cross hole on the outer tube. This arrangement functions as a mechanical fail-safe should the towed member be grossly beyond the drawbar""s rated capacity such as, by pulling a trailer that is too heavy or by attempting an unusual tow truck maneuver.
High hysteresis elastomeric sleeves are compressed and contained between the inner tube and outer tube to provide total isolation from noise and/or vibration that may be conducted from one tube to the other during typical operation. The elastomer functions to dampen the forces imposed upon the tow vehicle by the inertia of the towed trailer. Also, they may further damp the vibrations that emanate from the trailer and conducted via the drawbar and hitch pin to the towing vehicle. Also, many of these vibrations are caused by uneven road surfaces or by the shifting of cargo, such as, livestock, or other carried cargo.
All of the exposed metallic surfaces of the drawbar are treated, thereby being protected from corrosion by multiple step surface coatings.
The installation of this improved isolating drawbar is accomplished by sliding the tow vehicle""s receiver tube into the drawbar""s receiver cavity and securing it, preferably, by using the newly designed damped hitch, or alternatively, by using a commonly available hitch pin. Thus the installation requires the same familiar operation that is currently used in practice for the installation of a rigid drawbar.